1. Field of the Invention
The present disclosure relates to a video signal processing system and method, and more particularly, to a system and method for tracking a subcarrier or a color burst signal.
2. Description of the Related Art
A display system, such as a TV set or a personal computer monitor, includes a device for processing video signals input thereto. FIG. 1 is a block diagram of a conventional video signal processing system 100, including an analog-to-digital converter 110, a burst separator 120, a phase comparison and frequency compensation unit 130, and a Y/C separating and demodulating unit 140.
The analog-to-digital converter 110 converts an input analog video signal into a digital signal and outputs the digital signal to the burst separator 120. The input analog video signal can be a CVBS (Composite Video Blanking Sync) signal. The CVBS signal 200 includes a front porch signal 210, a horizontal synchronization level signal 220, a back porch signal 230, and an active video signal 240, as shown in FIG. 2.
The burst separator 120 extracts a color burst signal in the back porch signal from the converted digital signal. The phase comparison and frequency compensation unit 130 tracks a burst signal from the color burst signal extracted by the burst separator 120. The Y/C separating and demodulating unit 140 extracts a luminance signal Y and a chrominance signal C from the converted digital signal using the frequency or phase of the burst signal tracked by the phase comparison and frequency compensation unit 130 interpolates the luminance signal and the chrominance signal and generates color signals suitable for a display, such as a Liquid Crystal Display (LCD). Specifically, the Y/C separating and demodulating unit 140 generates the color signals in the form of RGB color signals, or a luminance signal Y and chrominance signals Cb and Cr, in accordance with the particular standard used by the display. Images corresponding to the color signals are displayed on the display for a user to see. The conventional video signal processing system 100 is described in detail in U.S. Pat. No. 5,355,171.
The phase comparison and frequency compensation unit 130 tracks the burst signal using a Phase Locked Loop (PLL) or a loop filter. The burst signal includes information for extracting the chrominance signal based on a modulation scheme. The phase of the burst signal included in the CVBS signal may represent chrominance information in the National Television System Committee/Phase Alteration By Line (NTSC/PAL) system, and a variation in the frequency FSC of the burst signal may represent the chrominance information in the SECAM (Sequential Couleur A Memoire) system. Consequently, the chrominance signal cannot be obtained when phase information or frequency information tracked by the phase comparison and frequency compensation unit 130 contains errors.
However, the conventional phase comparison and frequency compensation unit 130 tracks one of the phase information and frequency information of the burst signal. The currently tracked phase or frequency information is compared to phase or frequency information tracked in a previous horizontal scan period. When there is a difference between the currently tracked phase information and the previously tracked phase information, the tracked information is updated to yield new information compensated by the difference. Here, even if the tracked phase corresponds to the phase of the burst signal at the starting point of the burst signal, it may not coincide with the phase of the burst signal at the end point of the burst signal because the frequency of the tracked information may not correspond to the frequency of the burst signal.